Forgot to mention, Joe the programmer made placeholder graphics using the editor built into Play My Code, so he could get the games ready while waiting for the final artwork from me- saved loads of time!

To answer your question, I used Photoshop on Mac to do the visuals but I tried to use a lot of different techniques- some of the graphics are vector art, some hand-drawn on a graphics tablet and some a combination of the two (plus, a photo of my hand!)